Plate-type heat exchanger

ABSTRACT

A plate-type heat exchanger in which the stamped plates have corrugated central portions flanked by noncorrugated inlet and outlet zones. The sinusoidal and trapezoidal section corrugations of the plates are offset by half the distance between the corrugations to form uniform cross section channels throughout the stack. The plates are bonded together along marginal portions and at their bearing faces with a thermosetting synthetic resin.

United States Patent Hubbard 944 .lendrassik..m..t..... 952 Collins............ .......v.....

l/l966 Steinetal.....................

Primary Examiner- Frederick L. Matteson Assistant Examiner-Theophil W. Streule At!orney--Karl F. Ross nm a" mm m a n WK 1 27 3 55 9 99 HHHHH 05 6 3 00 54 390736 6658 369 92 .3 22223 v. n m e G .t 0 h t o b h c m m I0 81 uh H 1 I 1] nm 6 a M 3 m m m JA 7N] B o d m N. e Mmme v HM h AF? 3 N 7 224 [73] Assignee Linde Aktiengesellschah Wiesbaden, Germany [32] Priority Nov. 3, 1967 [33] Germany R E G N A H C& h EF mm E w u m ED mm S mm I MC P3 A plate-type heat exchanger in which the stamped plates have corrugated central portions flanked by inlet and outlet zones. The sinusoidal and trapezoidal section corrugations of the plates are offset by half the distance between the corrugations to form uniform cross section channels throughout the stack. The plates are bonded d C 2. A w r m w m m A n 78 a1. 6 mN w ls m 12mm F [50] Field together along marginal portions and at their hearing faces with a thennosetting synthetic resin.

C s m m A m R E M PATENTEU JUL 6197! SHEET 1 OF 6 IN VENTORS Johann Huber Leonhard Porh Attorney PATENTEDJUL slsm 3,590,917

SET 2 BF 6 INVEN'I'ORJ Johann Huber y Leonhard Pofh (.Karl g RJM Attorney PATENIEDJUL 6l97| 3590 91 saw 3 BF 6 IN VENTORS Johann Huber Leonhard Pofh A fR ss Attorney PATENTEUJUL BIS?! 3.590.917

SHEET b 0F 6 INVEX'I'URS Johann Huber Leonhard Po Ih Attorney PATENH-IUJUL SIQTI 3.590.917

saw 5 BF 6 INVENTORS 5 Johann Huber Leonhard Porh Attorney PATENTEU JUL el SHEET 6 0F 6 THERMOSETT ING S u wh 6 w mH w m V 0 o N P gr I" h m M 00 JM 0 e L PLATE-TYPE HEAT EXCHANGER The present invention relates to plate-type heat exchanges and, more particularly, to heat exchangers for low-temperature applications such as air or gas liquefaction and/or rectification.

lt has been common practice for some time to provide socalled plate-type heat exchangers in which a plurality of stacked plates are formed with channels or the like and are assembled by soldering to provide two or more sets of compartments separated by the plates through which heat exchange occurs.

When plate-type heat exchangers" are concerned, they usually are characterized by rectangular plates which define the heat transfer partitions as well as the channels for the respective media, as opposed to tube-type heat exchangers in which a plurality of tubes or pipes carry one medium while the surrounding space is filled with the other medium.

An economical manner of making plate-type heat exchangers has been to shape the plates and assemble them together so that at least at the peripheral zones of the plates or the boundaries of the channels a hermetic seal is provided. To this end, prior-art techniques have generally made use of solder seals between the contacting faces of the stack, the molten solder being drawn by capillarity into the region of the interface to render the seal gastight. To solder the plates together, it has been the practice to make use of molten or fused salt baths, heated salt beds and the like to bring the plates to the soldering temperature. Such systems have led to relatively high production costs with the need for expensive equipment, etc. Even more significant, however, is the fact that this soldering technique very often allowed fluid leakage through insufficiently soldered portions which were inaccessible and thus could not be repaired after assembly of the plates. As a result, entire assemblies were discarded or torn apart with manufacturing delays and the like. In addition, the solder joints, if defective, were sensitive to the thermal stresses applied to the plates when such heat exchangers were used for low-temperature technology, e.g. for air or gas liquefaction and/or rectification.

It is the principal object of the present invention to provide an improved heat exchanger of relatively low cost and simple construction with particular utility in cryogenic installations.

A further object of this invention is to provide an improved plate-type heat exchanger of high efficieney and low cost which obviates the disadvantages of earlier heat exchanger devices of the same general type.

It has now been found that an improved plate-type heat exchanger, particularly satisfactory for use in low-temperature processes, can be made at relatively low cost and yet be of high heat exchange efficiency, when the heat exchanger is constituted of a stack of heat exchange plates deformed into an undulating cross section at least along a center region of the plates and juxtaposed such that the longitudinally extending undulations of each plate are transversely offset from those of the adjacent plate by approximately one half of the distance between corresponding undulation peaks or troughs (i.e. one half the wave length or period of the undulations) so that the undulations define channels of uniform cross section, the stack being assembled by an adhesive at the contacting or closest approach regions of the plates, e.g. at the periphery or the undulations thereof.

When the term adhesive" is used here, it will be understood that reference is intended to synthetic resin bonding materials, especially thermosetting synthetic resins such as epoxy resins or epoxyderivative resins. it has been found, surprisingly, that the use of such adhesives in place of the solder used heretofore is that the solder is substantially more sensi' tive to the surface condition of the plates and often fails to wet the latter even when the assembly is brought to the flow temperature of the solder. Furthermore, solder bonds effectively only when the assembly has cooled below the hardening temperature of the solder so that the bond itself is not formed at elevated temperatures which, however, may give rise to surface films repelling the solder. It has now been observed, with much surprise, that the use of thermosetting synthetic resins, especially epoxy resins, permits bonding to the metal surface whether they are pressed together tightly or not, whether they become coated with films or not, and whether or not the resin is considered to be capable ofwetting" the metal. As a purely practical matter, it has been found that such adhesives indeed wet" the metal as they approach their cooling temperature in spite of the fact that at ambient temperatures that may not have appeared to be capable of wetting the plates.

The resulting plate-type heat exchanger is substantially less expensive than soldered heat exchangers, not only because of the lower cost of the adhesive, but also because the defect rate decreases with the use of such adhesives. The apparatus used in the manufacture of the heat exchanger is of lower cost and the process steps are of decreased complexity.

According to another aspect of the present invention, the undulating profile or cross section of the heat exchanger plates is substantially periodic in the manner of corrugations which may be generally sinusoidal or angular when, for example, the undulations have trapezoidal profiles. At any rate, it is found that best results are obtained when the troughs and crests of the undulations are geometrically similar and the undulations of the plates of the stack are identical. In accordance with one aspect of this invention, the crests on one side of one of the plates of the stack bear directly upon the crests at the opposite side of the juxtaposed plate, the latter crest forming floors of troughs in line with the first-mentioned crests.

When troughs and crests of trapezoidal profile were assembled in this manner, the duct for the several heat exchange fluids will have a generally hexagonal cross section, especially when the offset of the crests or the troughs of juxtaposed mutually adjacent plates is one half the intercrest spacing and one half the intertrough spacing.

An advantage of this construction, wherein each crest abuts the floor of the trough of an adjoining compartment and vice versa, is that the assembly has a honeycomb structure capable of supporting the assembly mechanically against pressure differentials which may develop between the fluids traversing the respective channels. Furthermore, spacers within the channels can be avoided or omitted and vibrations in the form of alternate contractions and expansions of the channels are prevented. Since there is little change in flow cross section as a result of pressure differentials across the walls of the heat exchanger, the device is particularly suitable for use as a reversing heat exchanger in low-temperature technology wherein, for example, a gas to be liquefied is passed through one set of channels and impurities condensed therefrom as the gas traverses these channels in one direction. Frequently, a warm gas must flow through the same channels in the opposite direction at a subsequent stage while some arrangements provide for temporary evacuation of the channels and the use of sparging gases at various stages of the process. Since all of the channels have the identical flow cross section in the system of the present invention, such use of the heat exchanger as a reversing or reversible heat exchanger is facilitated.

When the undulate plates have sinusoidal profiles, the zone of contact between the crest of one plate and the floor of the trough of an adjacent plate lies substantially along a line. It has been found that such structures are susceptible to deformation, especially when the adhesive is applied only along marginal zones of the heat exchanger plates. Consequently, the adhesive should also be applied at the crest-contacting surfaces of the sinusoidal profiles.

When trapezoidal profiles are provided, contact occurs along the small base of the trapezoid between the crest and trough of the adjacent plates; the adhesive thus may be applied to the crests and troughs as well as along the marginal zones of contact. The adhesive at the crests is not vital but may be used if additional stability is desired. It may be noted, however, that it is the preferred arrangement to apply the adhesive at all contacting surfaces. This ensures total lack of movement of the plates of the heat exchanger relatively to one another both in their planes and transverse to their planes and also precludes any fluid flow transverse to the crests of the undulations.

According to another aspect of this invention, the plates have a generally rectangular configurationwith the flow channels defined between and within the corrugations extending in the longitudinal direction of the rectangle. Advantageously, the u'ndulate portion of each plate is formed by the central re gion thereof and is flanked at the small ends of the rectangle by an inlet and outlet zone free from the undulations and extending practically over the entire width thereof, these zones being identical on all the plates. The plates are thus not only mutually coextensive but preferably have coextensive central corrugated zones and coextensive inlet and outlet zones at either end of theu ndulatin'g zone. These inlet and outlet zones are provided with guide structures, e.g. bosses which,together with the continuous crests and troughs produce a right-angle flow at each end of the undulate zone. Thus the incoming fluid is bent through9 at'the inlet zone and traverses the undulating'zone before being diverted through 90 again at the outlet zone. The result is a Z-shaped or U-shaped path for the heat exchange fluid. In the latter case,the inlet and outlet openings may be located at the same longitudinal side of the rectangle.

As has been observed, the inlet and outlet zones of 'each plate are not corrugated or of wave configuration and are subject of deformation as a result of any pressure differential across these plates or between the heat exchange fluids. The bosses, which are spaced apart in both the longitudinal and transverse directions at the inlet and outlet zones of the plates and'are of frustoconical configuration, bear upon the adjoining plates and reinforce the stack against platedeformation under this pressure differential. The bosses of each plate are alternately recessed therein and pressed outwardly therefrom to opposite sides of the plate for engagement with theinverse- ,ly shaped bosses of the adjoining plate. The circular contact surfaces of these plates may also be provided with adhesive to bond the plates together. Additionally, the bosses constitute projections in the path of the heat exchange fluid and thus increase the turbulence of the fluid flow and the heat exchange efficiency. Also, one or more bores or holes can be provided in the inlet and/or 'outlet region by means of which the heat exchange medium can be delivered to the respective sets of channels. Fluid supply in this manner is analogous to that of the radiator art.

To facilitate assembly of the heat exhanger and increase the structural strengththereof, the marginal regions of each plate are provided with a profiled ridge over part or all of the periphery, the ridge being pressed transversely from the plate during the stamping operation which forms the crests and troughs and the bosses. In the spaces between two interconnected plates, profiled bars of a cross section corresponding to these passages, can be inserted and bonded with a thermosetting adhesive to the plates. Theends of the heat exhanger can be supported in part by comblike structure whose arms are inserted into the openings between each pair of two interconnected plate edges. The profiled bars and comb structures increase the rigidity of the assembly as well as the fluid tightness thereof. It should be pointed out that the profiled reinforcing bars or combs should be disposed so as not to obstruct the openings for introduction or removal of the fluid. They may, however, act as supports for housing structures designed to enclose the stack of plates and to introduce or remove the fluids from the channels.

To increase the structural strength of the unit, we provide that the stack of relatively thin sheet metal plates is flanked along their broad surfaces by a pair of relatively'thick-walled cover plates whose surfaces turnedaway from the stack are smooth or flat while the surfaces of these thick plates turned toward the stack are corrugated or undulated corresponding to the corrugations of the plates against which they bear.

According to still another feature of this invention, the stack of plates forming the body of the heat exchanger is composed of plates of unit construction and is symmetrical about a median plane through the stack whereby the plates may merely be reversed with respect to one another, stacked, cemented together with adhesive and assembled into the desired configuration. Morcover, it has been found to be advantageous to secure between plates of each pair defining an array of channels or passages for the fluids with their respective corrugations, throughs or crests, spring-ribbed sheet metal strips, preferably of profiled cross section, which increase the turbulence'of the fluids passing through the channels. The strips may be of sinusoidal configuration or trapezoidal configuration, as willbe apparent hereinafter, and formed with flanks generally parallel to the direction of fluid flow through the channel and to the crests and/or troughs in which they are housed. These flanks'may extend along the channels to subdivide them into a plurality of parallel compartments and may be formed with pockets, projections, protuberances or other formations which interfere with laminar flow along these flanks and promote turbulence.

The, plates of the stack of the present heat exchanger are preferably formed of a material of high thermal conductivity which also is usually stamped, e.g. copper, brass, aluminum or aluminum alloy. Best results are obtained with aluminum and its alloys although chromium-nickel-steel plates may also be employed.

The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing, in which: i

FIG. 1A and FIG. IB are plan views from the top ofa lower plate and upper. plate, respectively, forming a stack in accordance with the'present invention for a plate-type heat exchanger;

FIG. 2 is a perspective view in exploded form of the plate stack of a heat exchanger inaccordance with another embodiment ofour invention; i

FIG. 3 is a view similar to FIG, 2 illustrating yet another embodiment;

FIG. 4 isa perspective exploded view of the plate stack of a heat exchanger according to this invention wherein one fluid describes a U-shaped path while the other fluid a substantially straight path; I i FIG. 5 is a cross-sectional view through a plate-type heat exchanger embodying thepresent invention;

FIG. 6 and FIG. 7 are fragmentary perspective views of heat transfer elements adaptEd to be used in the system of FIG. 5;

FIG. 8 is an enlarged cross-sectional view of a fragment of a heat exchanger stack showing the use of the thermosetting resin to bond the plates together;

FIG. 9 is a partial perspectlve view of another plate assembly;

FlG..l0 is a view similar to FIG. 8, showing the application of the principles of the present invention to a heat exchanger using plates of sinusoidal profile;

FIG. I1 is a cross-sectional view of another embodiment of this invention;

FIG. 12 is a plan view of a plate according to another feature of this invention;

FIG. 13 is a fragmentary elevational view diagrammatically illustrating a method of assembling and stiffening the stack; and

FIG. 14 is a crossssectional view of the boss arrangement of the plates in FIGS. 1-4..

In FIGS. 1A and IB, we have shown a pair of plates 1 and 11 for a plate-type heat exchanger in which the plates may be stacked (FIG. 5 or 8), reinforced by the fingers of a comb support (FIG. 13) and bonded at its boss structure (FIG. 14). The lower plate of this embodiment, shown in FIG. 1A, is a pressed or stamped rectangular sheet metal body 1 havinga central zone C spaced inwardly from the narrow ends of the plate by the zones l and 0 respectively constituting the inlet and outlet sides of the plates and which are free from corrugations. The central zone C of the plate is formed with a plurality of mutually parallel transversely spaced corrugations of trapezoidal cross section both in the longitudinal plane P and in the transverse plane P, the crests 3 of the corrugations rising out of the plane ofthe paper in FIG. 1A.

The narrow base of each trapezoid 3 rests upon the downwardly turned narrow face of the troughs of an upper plate. The trapezoids are open at their wide bases. At the inlet side I, the plate 1 has a zone 4 which is free from the corrugations 2, 3 and is provided with stamped bosses 6 which rise out of the plane of the paper and are of frustoconical configuration as shown, for example, in FIG. 14. The bosses 6 have a height corresponding to that of the crests 3.

Along part of the periphery of the plate 1, we have formed sealing ridges 7, 8, 9 and 10, which completely surround the formations 2, 3, 6 except at inlet 18 and outlet 19 along the right-hand longitudinal side of plate 1. The sealing surfaces 7-10 may be coated with adhesive (FIG. 11) and are of the same height as the bosses 6 and the crests 2 and 3. A similar array of bosses 6 is provided at the noncorrugated outlet side as represented at 5.

The upper plate 11 (FIG. 1B), which is designed to be placed upon the plate 1 of FIG. 1A, may be identlcal with plate 1 but rotated in its plane through 180. When the plate 11 is then placed upon the plate I, the raised surfaces 7-10 of the latter abut the nonraised sealing surfaces 12, 13, 14 and 15 of plate 11 and are hermetically sealed relatively thereto with a thermosetting adhesive as described in connection with FIGS. 8-12 and 14.

The crests 3 of plate 1 are brought to bear against the floors 16 of plate 11 so that hexagonal channels are formed as shown in FIGS. 5 and 8. The bosses 6 are so constituted that they alternately project from the surface (boss 6) or are recessed therein (6"); thus the recessed bosses 6" of plate 11 rest upon the upstanding bosses 6 of the plate 1 (see FIG. 14).

A layer TI of thermosetting synthetic resin is provided between the juxtaposed sealing faces of these bosses. Plates 1 and 11 are hermetically sealed with this resin over all of their mutually contacting surfaces. The plates can be stacked without separators and the gaps between the plates formed by the corrugations 2 charged with the heat exchange media.

In the system of FIG. 1, in which plate 11 is placed upon plate 1, one heat exchange medium is introduced at 17 and passes through the inlet 18 about the bosses 6 and is then deflected through the spaces between the crests prior to deflection outwardly through the outlet 19. The result is a U- shaped flow pattern. A countercurrent flow of the other gas stream along the opposite surfaces of plate 11 is represented by arrows 20. The gas here passes into the assembly through inlet 21 and then flows along the valleys or troughs 16 prior to emerging from the system in a U-shaped pattern. The fluid stream, in each case, is deflected twice through angles of 90.

In FIG. 2, an exploded view ofa modified stack of plates has been illustrated, the plates 25, 26, 27 and 28 being of totally identical configuration with every other plate being rotated in its plane through 180". As in the system of FIG. I, the marginal portions 29 and 30 of plate 26 project toward the corresponding marginal portions 33 and 34 of plate 25 by a distance I equal to one half the combined altitudes a of the bosses 37, 38 and, therefore, the altitudes A of the channels formed between the plates (FIG. 5). The plates 25 and 27 and the plates 26 and 28 thus are oriented similarly. When the plates 26 and 28 are assembled together, the boundary surfaces 29, 30, 31 and 32 of the plate 26 engage the boundary surfaces 33, 34, 35 and 36 through layers of thermosetting adhesive applied as shown at TP to the boundary portions in FIG. 12. The troughs 16 of the trapezoidal corrugations 2 of plate 25, which have the same configuration as the correspondingly numbered portions of FIG. I, bear against the crest 3 of the undulations of the opposite plate, thereby forming between these plates six-sided channels as shown in FIG. 5.

The noncorrugated inlet and outlet sides 4 and 5 of the plates 25-28, are provided with the bosses 37 and 38 which correspond to the bosses 6, 6', 6", and which alternately stand out from the plate or are pressed rearwardly therefrom. The bosses 37 of plate 26 for example, bear against the bosses 38 of plate 25 (see FIG. 14). This construction ofthe plate allows each plate to rest against the neighboring plate at a multiplicity oflocations, thereby rendering the entire assembly substantially resistant to pressure differentials between the fluids.

The adhesive is preferably applied to the plates over all of their hearing locations and the system thereafter assembled and subjected to heat treatment at the curing temperature of the resin.

In the openings 40 between the pairs of plates, there are provided reinforcements in the form of the arms of a comb 101 or as profiled rods which fill the space between the surfaces 41 and 29 of plates 26 and 27, (see FIG. 13). Manifold chambers are provided at 103. Similar arms can be received in the openings 102 inwardly of the marginal portions 29 and 33 or 39 and 40 of the pairs of plates. The arms 100, of course, have a cross section identical to that of the openings in which they are received. Suitable profiled bars for insertion in these openings have been shown at 91 and are received in the openings in the narrow end sides of the stack. The thermosetting bonding agent is applied to the bearing surfaces of the plates, the profiled bars 91 and/or the arms 100 of the assembly. The bars 91 (FIG. 5) increase the compressive strength, stiffness and fluid tightness of the assembly. The profiled bars neednot extend the full length of the openings in which they are inserted to accommodate inlets and outlets for the heat exchange medium which, in the embodiments ofFlG. 2, is represented by the arrow 42 and passed in a U-shaped path from the inlet openings 43 to the outlet openings 44 between the plates.

The other heat exchange medium is represented by the arrow 45 and flows along an inserted U-shaped path through the inlet 46 to the outlet 47 between the plates 26 and 27 in countercurrent to the first-mentioned medium 42. The collecting and manifold chambers of the heat exchanger are represented at 103 in which they are shown to be attached to bosses or other formations on the profiled bars 91 and/or the support comb 101. The chambers may be hoods welded to these members (FIG. 13).

The flow cross section of the fluid mediums 42 and 45 can be interchanged for operation of the heat exchanger as a so called reversing exchanger" inasmuch as the flow cross section between each pair of plates is identical. The two mediums which are passed in heat-exchanging relationship, may have inlets in the form of two manifold chambers on the left side of the stack and two manifold chambers on the right side of the stack respectively for the functional interchange of the mediums in their flows through the respective channels.

The heat exchanger stack illustrated in FIG. 3 comprises the plates 50-53 which operate with three different mediums. The plates are basically similar to those of FIGS. 1A, 1B and FIG. 2 and have trapezoidal section longitudinal undulations over the central region as described in connection with these Figures. The inlet and outlet ends of the plates are free from such crests or troughs but are formed with frustoconical bosses which bear upon one another and are bonded together by the thermosetting synthetic resin.

When the plates 50 and 51 are bonded together at their peripheral surfaces 54-57 and 58-61, respectively, the usually confronting bosses and crests are similarly joined. Plates 50 and 51 define between them a U-shaped flow path wherein a first medium (represented by arrow 62) enters at an inlet 63 and exits through an outlet 64 between this pair of plates. The boundary surfaces 58-61 of plates 51 are so contoured that between the plates 51 and 52 a linear flow path exists for a second medium 65 which, when the plates are bonded together by the thermosetting resin, cannot mix with the medium 62 and which enters at the narrow side 66 while departing at the narrow sides 67 of the assembly. Plate 50 corresponds to the plates 25 and 27 of FIG. 2 while plate 53 corresponds to plates 52 but is rotated in its plane l80 with respect to the other. The space between plates 52 and 53 can sustain the flow of a third medium 68 in the same flow direction as medium 65. Between plates 53 and a subsequent plate of the stack (not shown), the channels are formed as in plates 52 and 50 and a flow path is provided for the first medium 62.

The heat exchanger stack of FIG. 3 can be used with considerable advantage in air rectification wherein air, oxygen and nitrogen constitute the first, second and third medium. Since the flow cross sections of all the plates are identical, the channels my be used interchangeably for reversing heat exchanger relationship.

The stack of FIG. 3 requires two manifold chambers for the medium 62 and 68 on the right and left sides of the unit respectively and a further pair of collecting chambers along the upper and lower sides of the stack. When the stack is modified so that plate SI is rotated in its plane through 180, thereby providing its inlet and outlet openings on the right rather than the left side of the unit, four mediums can be used, e.g. air, nitrogen, oxygen and a turbine gas which is to be heated for operating a low-temperature expansion turbine. The latter stack requires eight collecting chambers, two at each longitudinal side and two at each of the narrow sides of the plates.

The stack of FIG. 4 provides the four plates 70, 71, 72 and 73 of which plates 70 and 72, and plates 7I and 73 are identical in form and position. The direct stacking of the plates (within intervening layers of thermosetting synthetic resin to bond them together as described in connection with FIG. 2) forms a heat exchanger assembly in which gas flow paths as represented by the arrows 80 and 83 can be sustained. The trapezoidal corrugations 2 are pressed from the sheet metal plates and extend perpendicular to the plane of the paper but, with respect to the alternate plates, are offset from one another by half the intercorrugation distance. The boundary zone 74-77 of plate 71 bears against corresponding surfaces of plate 70 via the intervening thermosetting layer so that between plate 70 and 7I and between 72 and 73 U-shaped flow paths 80 are constituted, the inlet 78 and the outlet 79 being formed with interruptions in the marginal strip 74--77. Between plates 71 and 72, the superimposition of the plates produces a linear flow path as represented at 83 from the underside of the stack to exit at the upper side thereof. A platetype heat exchanger as shown in FIG. 4 has been found to be particularly suitable for use as an evaporator-condenser, e.g. in the upper column ofa double rectification column for the separation of air into nitrogen and oxygen in accordance with the Linde-Frankl rectification system. In this case, a central duct leads nitrogen vapor from the lower column to the heat exchanger as the first medium 80 to condense the latter while liquid oxygen passes directly through the unit and is vaporized. When the thermosetting resin may be sensitive to deterioration in contact with liquid oxygen, the oxygen flow chamber may be closed by ultrasonic welding.

FIG. 5, as has been noted, shows the honeycomb section of a platelike heat exchanger in accordance with the invention and in which the broad open bases of the trapezoid register with one another to form hexagonal channels 90. The crest of each one of the corrugations of a lower plate is bonded to the floor of the trough of a plate superimposed thereon. Each of the channels may have a cross section with a hexagonal side length S of 2 to 3 mm. Between each pair ofjuxtaposed-plate edges and the edges of an adjacent pair, there are formed openings which receive the profiled rods 91 or the arms I mentioned earlier. Furthermore, at each of the broad ends of the heat exchanger stack, parallel to the plates, there is provided a relatively massive terminal plate 92 whose outer surface 92a is flat while the inner surface is formed with solid corrugations 92b which are received in the initial plate 920. The result is a more rigid heat exchanger structure and a fiuidtight seal.

Lit

To increase the heat exchange surface area, one or more channels may be provided with a longitudinally extending heat transfer element 93 or 94 shown in enlarged scale in FIGS. 6 and 7. The sheet metal elements, which may span the width of the channels, act as partitions whose flanks 93a, 93b and 94a subdivide the channels into compartments on opposite sides of these partitions. The partitions are provided with pockets 95, 96 which project into the path of the fluid to produce turbulence. A sinusoidal heat transfer element is shown at 94 while the element 93 is of trapezoidal configuration.

In FIG. 8, I have shown the honeycomb structure of FIG. 5 wherein contact is made between the small bases of the trapezoidal channels. The synthetic resin layer TP is here coextensive with the small-base portions I08 and bonds the plates I09, 110, III and 112 together. As has been pointed out, a sheet metal partition 113 can be introduced between the small bases I08 of the trapezoids, with the usual intervening layer TP. of thermosetting synthetic resin. The undulating portions 115 and M6 on opposite sides of the plate I13 may be perforated as shown at 117 (FIG. 9) or provided with teeth (FIG. I l).

It has also been pointed out that the corrugations may be of generally sinusoidal configuration as is shown, for example, for the plates 118, I19 and I20 in FIG. 10. At the mutually approaching crests and troughs of this assembly, strips TP of thermoplastic synthetic resin are provided to bond the stack into a heat exchange unit. Between the crests and the troughs, a partition 121 can be disposed (FIG 11) and bonded to the plates I22 and 123 by thermosetting synthetic strips TF Again, the plates may be perforated or formed with teeth as shown at 124 in FIG. 11.

FIG. I2 has shown a plate to be stacked with similar plates in a heat exchange structure and herein the marginal edge 125 of the plate is continuous but is provided with the thermoplastic adhesive coating previously mentioned. A pair of bores 127 at the uncorrugated inlet side ofthe plate 128 serve to admit the heat exchange fluid (129) and permit it to pass the bosses I30 which extend alternately upwardly and downwardly from the plane of the plate. The flow paths (arrows 13]) are of Z-shaped configuration and lead to the outlet bores 132.

EXAMPLE A plate-type heat exchanger using the configuration of FIG. 2, is assembled so that the six-sided longitudinally extending channel have a hexagonal side length S of 3 mm. or 2 mm. in tests A and B while the wall thickness s of the plates is 0.3 mm. and 0.2 mm. The plates were composed of aluminum and eemented together with epoxy heated at the curing temperature in the usual manner. The following table lists the parameters and the results achieved:

Passage height, mm 2.6 1. 73 Number of ribs per m. (meter) of plate width 111 166 Hydraulic diameter, mm 5. 2 3. 5 Relative free space, percent 86. 2 86. 2 Free throughflow cross-section per m. (meter) of plate width and plate length and per passage, ml .0. 00215 0.00102 Primary surface area per m. of plate width and plate length and per passage, m1 1. 33 I. 33 Rib surface area per m. of plate width and plate length and per passage, ml 0.67 0. 67 Volume of heat transfer area, mfi/mfl. 0. 00145 0.00097 Weight of heat transfer area, kg./m. 0. 54 0. 36

The improvement described and illustrated is believed to admit of many modifications within the ability of persons skilled in the art, all such modifications being considered within the spirit and scope of the invention except as limited by the appended claims.

We claim:

l. A plate-type heat exchanger, comprising a stack of at least two pairs of geometrically similar and registering rectangular plates having congruently registering outlines, each plate being formed with a plurality of transversely spaced corrugations parallel to its longitudinal edges and projecting out of the principal plane of the plate over only a central region thereof whereby the corrugation crests define a secondary plane parallel to the principal plane of the respective plate, each plate further having a pair of substantially noncorrugated regions at opposite ends of said central region lying in said principal plane and forming fluid distribution compartments com municating with troughs between the respective corrugations the corrugations of each plate being transversely offset from the corrugations of adjacent plates by about half the transverse spacing of the corrugations, one plate of each pair being formed with first edge portions lying in its principal plane and second edge portions lying in its secondary plane while the other plate of the pair is provided with second edge portions lying in its secondary plane and sealed to the first edge portions of said one plate of the pair while defining openings along said edge portions communicating with the compartments of the respective pair; and means for feeding fluid through said openings of each pair and between said pairs of plates.

2. The heat exchanger defined in claim 1 wherein said substantially noncorrugated regions of the plates of each pair at opposite longitudinal ends of said corrugations are formed with frustoconical projections reaching from each plate of the pair into engagement with the projections of the other plate of the respective pair whereby said projections define passages between them communicating with said compartments.

3. The heat exchanger defined in claim 2 wherein said corrugations have flat surfaces each engaging a flat surface of a trough of an adjacent plate of another pair. 

1. A plate-type heat exchanger, comprising a stack of at least two pairs of geometrically similar and registering rectangular plates having congruently registering outlines, each plate being formed with a plurality of transversely spaced corrugations parallel to its longitudinal edges and projecting out of the principal plane of the plate over only a central region thereof whereby the corrugation crests define a secondary plane parallel to the principal plane of the respective plate, each plate further having a pair of substantially noncorrugated regions at opposite ends of said central region lying in said principal plane and forming fluid distribution compartments communicating with troughs between the respective corrugations, the corrugations of each plate being transversely offset from the corrugations of adjacent plates by about half the transverse spacing of the corrugations, one plate of each pair being formed with first edge portions lying in its principal plane and second edge portions lying in its secondary plane while the other plate of the pair is provided with second edge portions lying in its secondary plane and sealed to the first edge portions of said one plate of the pair while defining openings along said edge portions communicating with the compartments of the respective pair; and means for feeding fluid through said openings of each pair and between said pairs of plates.
 2. The heat exchanger defined in claim 1 wherein said substantially noncorrugated regions of the plates of each pair at opposite longitudinal ends of said corrugations are formed with frustoconical projections reaching from each plate of the pair into engagement with the projections of the other plate of the respective pair whereby said projections define passages between them communicating with said compartments.
 3. The heat exchanger defined in claim 2 wherein said corrugations hAve flat surfaces each engaging a flat surface of a trough of an adjacent plate of another pair. 